# Macroid Formation in Salmacina stellaebayensis n. sp. From Mauritania's Baie de l'Étoile With New Insights on Mitogenome Evolution in Serpulidae (Annelida)

## TL;DR

A new serpulid species from Mauritania is described, with insights into its unique colony formation and mitochondrial genome evolution.

## Contribution

The first complete mitochondrial genome for the genus Salmacina is presented, along with new insights into Serpulidae mitogenome evolution.

## Key findings

- Salmacina stellaebayensis forms star-shaped macroid colonies in seagrass meadows.
- Mitogenome analysis reveals extensive gene order variation in Serpulidae.
- The species exhibits asexual reproduction and anterior regeneration, expanding known life-history traits.

## Abstract

Knowledge of serpulid diversity along the West African coast remains scarce. Here we describe Salmacina stellaebayensis n. sp. from the Baie de l'Étoile, Mauritania, a new macroid‐former generating striking star‐shaped pseudo‐colonies. Combining classical morphology with genomic data, we provide the first complete mitochondrial genome for the genus Salmacina and recover additional nuclear markers to clarify its phylogenetic placement within Serpulidae. Filograna and Salmacina form a taxonomically challenging group with uncertain generic boundaries. While additional data from operculate Filograna are needed, this study provides a valuable baseline and much‐needed molecular framework for future revisions. Comparative analyses of 17 serpulid mitogenomes reveal extensive variation in gene order, supporting the view that mitogenome plasticity represents a family‐level feature of Serpulidae. The new species also exhibits frequent asexual reproduction by budding and anterior regeneration, extending known life‐history diversity in the group. Together, these findings enhance our understanding of serpulid systematics, life history, and mitochondrial evolution, underscoring the value of integrative approaches in uncovering annelid biodiversity from underexplored regions.

We describe Salmacina stellaebayensis n. sp. from Mauritania's Baie de l'Étoile and provide the first complete mitochondrial genome for the genus Salmacina. The species forms distinctive macroid colonies in Cymodocea nodosa seagrass meadows, offering new insights into serpulid life history and habitat specialization. Phylogenetic and mitogenomic analyses clarify relationships within the family and highlight the remarkable variability of mitochondrial gene order across Serpulidae.